In the past, NASA tracking systems which provided range and bearing to targets have primarily been radar based. Advanced projects such as unmanned missions to the moon and Mars need automated rendezvous and capture (AR&C) to reduce operating costs and improve mission reliability. In the Tracking Techniques Branch at Johnson Space Center we are investigating the feasibility of a stereo digital image based sensor for AR&C. This system differs from traditional stereo systems in two significant ways. First, a passive cooperative target is used to calculate the range to three specific points as opposed to calculating a range map of the entire scene. The second unique feature is the image processing algorithms that are used to identify the target. In this paper the sensor's performance is compared to preliminary AR&C operating range and accuracy requirements. A theoretical error model is presented that predicts the sensor's accuracy as a function of range.